Date post: | 27-Dec-2015 |
Category: |
Documents |
Upload: | kerry-watts |
View: | 213 times |
Download: | 1 times |
Chemistry of Life
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lecture Outline
Basic Chemistry
o Elements – basic substances that make up matter
o Four elements that make up >90% of the human body
• Carbon (C)• Nitrogen (N)• Oxygen (O)• Hydrogen (H)
Basic Chemistry
o Atoms• Smallest unit of an element that has
chemical and physical properties of that element
• Smallest unit to enter into chemical reactions
• Structure Central nucleus Outer shells (energy levels)
Basic Chemistry
Subatomic particlesoIn nucleus
• Protons – positive charge
• Neutrons – no chargeoIn shells
• Electrons – negative charge
• Innermost shell can have 2 electrons
• Outer shells can have up to 8 electrons
• Number of electrons in outer shell determines the chemical properties of an atom
Basic Chemistry
o Atomic number• Number of protons in the nucleus• Denoted as a subscript to the lower
left of the atomic symbol
o Atomic weight• Number of protons plus the number of
neutrons• Denoted as a superscript to the upper
left of the atomic symbol
Basic Chemistry
o Mole• Measurement for the number of
atoms or molecules of a compound• Avogadro’s number 6.02 x 10 23
• Based on the number of atoms in exactly 12 grams of carbon atoms
Basic Chemistry
o Isotopes• Variations of one type of atom• Differ in number of neutrons
o Radioactive isotopes• Unstable isotopes that break down over
time• Releases detectable energy• Low levels of radiation can be used as
tracers• High levels of radiation can be harmful to
cells, but can also be useful
Basic Chemistry
o Molecules – form when atoms bond to each other
o Compounds – formed when atoms of different elements bond
Basic Chemistry
o Ionic bonds• Created by electrical attraction between
ions• Ions form when an atom gains or loses
electrons in its outer energy level to become stable
Positive ion—has lost electrons; indicated by superscript positive sign(s), as in Na+
Negative ion—has gained electrons; indicated by superscript negative sign(s), as in Cl–
• Can dissociate (separates into ions) when dissolved in water and are then referred to as electrolytes.
Basic Chemistry
o Covalent bonds• Created when atoms share electrons• Atoms can share more than one pair
of electrons Double bonds – atoms share two pairs of
electrons Triple bonds – atoms share three pairs of
electrons between them
• Polar covalent bonds result when there is an unequal sharing of electrons between atoms
2.2 Water, Acids, and Bases
o Water• Most abundant molecule in living
organisms• Is an inorganic molecule (does not
contain carbon atoms)• Is a polar molecule
Oxygen has a slight negative charge (δ-) Hydrogen atoms have a slight positive
charge (δ+) Attraction between slightly positive
hydrogen atoms and slightly positive oxygen atom results in hydrogen bonds
Water, Acids, and Bases
• Properties of Water1. Water is a solvent (liquid into which ions
are dissolved) Facilitates chemical reactions Molecules that dissolve in water are said to be
hydrophilic (water-loving) Molecules that do not dissolve easily in water
are said to be hydrophobic (water fearing)
Water, Acids, and Bases
2. Water molecules are cohesive and adhesive
Water molecules cling together (cohesion) because of hydrogen bonding
Water molecules cling to other substances (adhesion)
Water flows freely, allowing it to distribute evenly
Allows for transport
Water, Acids, and Bases
3. Water has a high specific heat capacity and a high heat of vaporization
Specific heat capacity is the amount of energy needed to change an object’s temperature by 1C
Heat of vaporization is the amount of energy needed to turn water into steam
Both allow for thermoregulation body temperature
Water, Acids, and Bases
o Acids and Bases• When water molecules break up, an
equal number of hydrogen ions (H+) and hydroxide ions (OH-) are released
• Acids are substances that release hydrogen ions (H+)
• Bases are substances that release hydroxide ions (OH-)
Water, Acids, and Bases
o Salt• A salt is an electrolyte formed when
an acid and a base are combined.• Water also forms.
• HCl + NaOH → NaCl + H2O
Water, Acids, and Bases
• pH Scale Used to indicate the acidity and basicity
(alkalinity) of a solution pH 7 is neutral (an equal number of
hydrogen ions and hydroxide ions are released)
pH above 7 is a base (more hydroxide ions are released than hydrogen ions)
pH below 7 is an acid (more hydrogen ions are released than hydroxide ions)
Water, Acids, and Bases
• pH of body fluids Normal pH of blood is 7.4 Acidosis – blood pH less than 7.35 Alkalosis – blood pH greater than 7.45 Blood pH needs to be maintained within a
narrow range Respiratory and urinary systems Buffers (chemicals that take up excess
hydrogen or hydroxide ions) Carbonic acid and bicarbonate ions
Water, Acids, and Bases
• Electrolytes Substances that release ions when put
into water The balance of electrolytes in the blood
affects the functioning of vital organs
2.3 Molecules of Life
o Four categories of molecules are unique to cells (called macromolecules)
• Carbohydrates• Lipids• Proteins• Nucleic acids
o Synthesis of macromolecules involves a dehydration reaction
o Breakdown of macromolecules involves a hydrolysis reaction
2.4 Carbohydrates
o The ratio of hydrogen (H) atoms to oxygen (O) atoms is approximately 2:1
o Function for quick, short-term cellular energy
Carbohydrates
o Simple carbohydrates• Low number of carbon atoms (3-7)• Monosaccharides
Glucose Fructose – found in fruits Galactose – found in milk
• Disaccharides Two monosaccharides joined together Sucrose (table sugar) – formed when
glucose joins with fructose Lactose – formed when glucose joins with
galactose
Carbohydrates
o Complex carbohydrates• Contain many glucose
(monosaccharide) units• Starch – storage form of glucose in
plants• Glycogen – storage form of glucose in
animals• Cellulose
Found in plant cell walls Humans are unable to digest (passes
through digestive tract as fiber)
2.5 Lipids
o Contain more energy per gram than other biological molecules
o Some function as long-term energy storage in organisms
o Do not dissolve in water o Consist mostly of carbon and
hydrogen atoms; contain few oxygen atoms
Lipids
o Fats and Oils• Formed when one glycerol molecule
reacts with three fatty acid molecules• Fats
Usually of animal origin Solid at room temperature Used for long-term energy storage,
insulation, and cushioning
• Oils Usually of plant origin Liquid at room temperature
Lipids
• Emulsification – cause fats to mix with water
• Saturated and Unsaturated Fatty Acids
Fatty acid (carbon-hydrogen chain ending with an acidic group –COOH
Saturated fatty acids have only single covalent bonds; lard and butter are examples
Unsaturated fatty acids have double bonds between carbon atoms wherever fewer than two hydrogens are bonded to a carbon atom; vegetable oils
Lipids
o Phospholipids• Contain a
phosphate group• Have a hydrophilic
head and hydrophobic tails
• Form backbone of cellular membranes
Lipids
o Steroids• Structure consists of four fused
carbon rings with attached functional groups
• Cholesterol Structural component of animal cell
membrane Precursor of several other steroids
2.6 Proteins
o Function of proteins• Fibrous structural proteins• Hormones• Muscle contraction• Transport• Protection• Enzymes
Proteins
o Structure of proteins• Made of amino acid subunits
Amino group Acid group R (Remainder) group – differentiates
amino acids
• Dipeptide – two amino acids joined together
• Polypeptide – three or more amino acids joined together
Proteins
• Amino acids joined together by a peptide bond
• Secondary structure – due to hydrogen bonding that may occur in a polypeptide
• Tertiary structure results from bonding between R groups
• Quaternary structure – arrangement of individual polypeptides in a protein containing more than one polypeptide
• Denaturation – irreversible change in the normal shape of a protein due to extremes in heat and pH
Proteins
o Enzymatic Reactions• Metabolism - sum of all chemical
reactions that occur in a cell• Enzymes (protein catalysts that
enable metabolic reactions) Named for their substrate(s) The shape of the active site determines
specificity of enzyme Many require cofactors that assist an
enzyme
Proteins
• Types of Reactions Synthesis Reactions
Two or more reactants combine Require energy Dehydration synthesis
Degradation (Decomposition) Reactions Larger, more complex molecule breaks down
into smaller, simpler products Hydrolysis reactions
Replacement (Exchange) Reactions – involve both degradation and synthesis
2.7 Nucleic Acids
o Huge macromolecules composed of nucleotides
o Nucleotides composed of 3 subunit molecules:
• A phosphate• A pentose sugar• A nitrogen-containing base
o Two classes of nucleic acids• DNA• RNA
Nucleic Acids
o Two classes of nucleic acids• DNA
Make up genes Contain pentose sugar deoxyribose Nitrogen-containing bases
Adenine (A) Thymine (T) Guanine (G) Cytosine (C)
Usually double stranded
Nucleic Acids
• RNA Intermediary in process of protein
synthesis Contain pentose sugar ribose The nitrogen-containing base uracil (U)
replaces thymine Usually single stranded
Nucleic Acids
o ATP (Adenosine Triphosphate)• Primary energy carrier in cells• Cells break down glucose and convert
released energy into ATP• Used when cellular reactions require energy• Breakdown of ATP results in one molecule of
ADP (adenosine diphosphate) and one molecule of inorganic phosphate
• ATP is rebuilt by the addition of inorganic phosphate to ADP
• One glucose molecule can build 36 ATP molecules